In order to understand the behavior and control of the tongue, the present study proposes to define the geometry of tongue motion in three spatial dimensions, for normal and deaf speakers, thereby comprising a map of tongue movement. The study also proposes to quantity tongue surface features that are biologically and acoustically meaningful, yet also collapse the data for use in statistical analysis. The specific aims are (1) to characterize 3D tongue surface behavior and decompose it into 6 primary cross-sectional movement patterns and 5 degrees of freedom, (2) determine the articulatory/acoustic interaction including the degrees of freedom of the tongue in normal speakers. Real- time multisectional ultrasound images of the tongue, electropalatography, and acoustic analyses will be used. The imaged tongue profiles will be examined statistically using three procedures: including curve fitting, and principal components analysis. This should yield mathematically rigorous parameters to distinguish significant differences across speech sounds and subject groups. To complement these measures, the tongue surface will be mapped in 3D space during sounds and pseudowords to highlight subtle movement and shape patterns. EPG measures will provide palatal shape and vocal tract cross-sectional area information. This study is important because the tongue, almost inaccessible to direct measurement, is poorly understood, leading to erroneous assumptions about its normal and disordered movement. Better knowledge of local and global adjustments in tongue shape and movement, due to both tongue biomechanics and task effects across speech sounds, will promote development of more effective treatment strategies for patients with tongue movement deficits.